...went through the same process you did on my '98 SOHC. PCV, EGR, check/replace/repair hoses, etc. Until..
Upper and lower intake manifold gaskets.
Upper and lower INTAKE MANIFOLD GASKETS.
UPPER AND LOWER INTAKE MANIFOLD GASKETS!!
UPPER AND...well, you get the idea.
Problem solved. Takes about an afternoon, no special tools. Take your time and remove/replace everything methodically. RA has Felpro U&L gasket sets for less than $50. There's a writeup somewhere here with pix.